Fluid impregnated capacitors made up of alternating electrode foil and synthetic resin film strips wound in a tight roll form have been difficult to impregnate with dielectric fluids because although a capacitor roll is wound with a certain degree of looseness, defined as space factor, the fluid must not only penetrate into the roll from the ends thereof, but must also penetrate the interfaces between film strips which stick together, and between film and foil strips which also stick together. In order to overcome this well known and common problem, a number of solutions have been proposed which relate to complex impregnation cycles and roughening of the foil and/or film surfaces by various surface disfiguration methods, including mechanical and chemical processes such as foil embossing, abrading, and coating, and film etching.
The problems associated with these solutions have been numerous, ranging from poor overall fluid impregnation and electrical test results, undesirable increase of thickness of the capacitor roll without correlation to the required space factor of the capacitor, and poor economics because of the additional processing required. More importantly the reliability and repeatability of acceptable electrical tests for capacitors produced from the usual manufacturing processes have been deleteriously affected by these prior solutions.